Concrete, once considered a rather lowly material suitable mostly for fabricating building foundations, bridge abutments, and other starkly utilitarian structures has in this century come into widespread use as a prime architectural constituent used in all sorts of structures ranging from the utilitarian such as highway surfacing, structural beams and arches to partly or completely decorative uses in building interiors, sculpture, patios and plazas.
The widespread growth and acceptance of concrete in such a variety of forms and roles rests upon a growing body of concrete technology which has developed to cope with the diverse requirements made of concrete. A variety of composite structures in which the well-known ability of concrete to accept high compressive loading has been married to the high tensile strength of materials such as steel has permitted concrete to assume a larger role in the construction of arches, domes, trusses, and elevated beams.
At the same time, the aesthetic appeal of concrete structures has been significantly enhanced by advanced techniques of forming, shaping and molding together with widespread application of a variety of surface treatments involving color and texture designed to add versatility and a pleasing appearance to the other advantages of concrete.
In promoting the broader uses of concrete as an architectural material, the developers of concrete technology have had to consider both aesthetics and economics in their attempts to compete with other material technologies.
A prime example of these concerns occurs in the use of concrete to form large horizontal expanses such as plazas and decks or any other uses where an extensive layer of concrete is supported upon an underlying ground surface or subsoil. Such large expanses are subjected to a variety of potentially destructive agents both during their pouring or laying as well as afterwards. As is well known, the curing of concrete involves a considerable evolution of both water and heat. The resulting mechanical stresses can be accommodated without fracture in relatively small expanses of concrete, but they pose serious hazards as the area becomes larger. Even after the curing of the concrete it is subjected to the stresses resulting from earthquakes and other geologic phenomena, such as shifting subterranean strata caused by variations in water table level or subsoil shrinkage caused by declining moisture content in years of drought, shock waves caused by the nearby movement of heavy vehicles, and probably other sources.
As a result, it has always been essential to provide at regular intervals through such expanses of concrete, a series of "expansion joints" at which the inevitable shrinkage and slight shifting of the concrete could be accommodated. Such expansion joints may extend completely through the concrete layer or, more commonly, only from the surface to a depth partway therethrough. In the latter case, the concrete layer, being thinner in the region of the expansion joint will crack at this point rather than randomly over the surface. Since the expansion joint usually includes means to maintain a water seal to prevent subsoil erosion despite the crack in the concrete beneath it, and since the expansion joint also hides the crack from sight, such joints provide a worthwhile means of accommodating the inevitable.
In earlier times, expansion joints were often made of organic materials such as asphalted felt or wood. However, with the passage of time, such materials naturally degrade due to the action of water, sunlight, and oxygen. As a result they become unsightly and unsound, and require too-frequent replacement. Moreover, they do not adequately seal the joint against seepage of water into the underlying soil where erosion can further damage the concrete layer.
Consequently, a new type of expansion joint has come into being, utilizing relatively stable and inert plastic materials which are cheaper, more durable, and ultimately more beautiful than the old materials. The plastic materials resist the action of the elements better than the former wood or felt joints, can be easily fabricated in complex shapes, are available in a variety of colors and finishes, and have been designed to provide a much more satisfactory seal against water seepage into the underlying earth once the concrete has fractured at the site of the expansion joint. A particular type of such expansion joint is thoroughly detailed and covered in my U.S. Pat. No. 3,871,787 issued Mar. 18, 1975 and entitled "Joint Structure for Concrete Materials and the Like".
Similar molded plastic structures may also incorporate a plurality of apertures on the top surface thereof leading to a central hollow chamber which then serves as a drain while continuing to function as an expansion joint. Structures of this general type are exemplified by U.S. Pat. No. 3,465,654 issued Sept. 9, 1969 and entitled "Drain Device".
If devices of the above types are to become fully accepted and their full economic and aesthetic advantages realized, it is necessary to simplify as much as possible their laying and interfacing with the adjacent and abutting concrete areas. The finished interface between these materials and the adjacent concrete must insofar as possible retain the smooth, aesthetically pleasing appearance and be reproducible with a minimum of skill and effort without resorting to complex procedures.
The joint structure detailed in my earlier U.S. Pat. No. 3,871,787 referred to above is placed in the concrete after the latter has been poured and spread, but before it has cured. Thereafter, the concrete is tamped, surfaced with a "bull float", and then troweled and grooved. Following these operations, it is necessary to "edge" the concrete where it abuts the expansion joint. The device of the present application is a tool designed to facilitate and improve the result of this edging operation.
Such tools have existed in the prior art, consisting basicly of one or a pair of blades secured to a frame, the blade or blades being shaped so as to form the surface of the concrete to any desired shape in the area where it abuts an expansion joint or any other septum in the surface of the concrete layer. However, such tools have in the past been less than ideal in their conception and have suffered from a number of design faults which rendered their use somewhat awkward and difficult.
In particular, in view of the wide variety of expansion joints, drains and other septa coming into use in concrete work provision needs to be made for adjustability and adaptability in the edging tool. Since the widths of the various joints may vary according to the design and intended usage, it is desirable that the edging tool provide for adjustment or adaptation to accommodate different widths of the septum or joint. Moreover, it is desirable that the shape produced at the edge of the abutting concrete layer be variable to accommodate different needs.
As noted above, the septum or joint is placed in the concrete while the latter is uncured and still wet, and a number of operations are performed prior to the edging operation adjacent the joint. As a result, the top of the joint is usually covered with a layer of concrete which must be swept away as a part of the edging operation.
Prior art edging tools have used resilient rubber wiping blades to achieve this purpose. However, the method of securing these blades in position and removing them from the tool when they need replacement or to permit edging without the wiping blades (for example as a finishing step) has been difficult.
In particular, the rubber wipers in the prior art have typically been held by various fixed clamps often involving set screws or similar means for securing the rubber wipers. Consequently, proper adjustment of the position of the wipers has been difficult to achieve, and removal and replacement of the wipers an unnecessarily tedious operation.